69 lines
2.9 KiB
Rust
69 lines
2.9 KiB
Rust
///
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/// Trying to get around "".into() for String values.
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/// Or "".to_owned().
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/// Or String::from("").
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/// Or "".to_string().
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/// Choose your church.
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///
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/// This is as far as you will get declaratively.
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#[macro_export]
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macro_rules! strinto {
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($struct:ident { $($field:ident : $value:expr),* $(,)? }) => {
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$struct {
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$(
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$field: $crate::strinto!(@convert $value),
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)*
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}
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};
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(@convert $value:literal) => {
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match () {
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_ if stringify!($value).starts_with("\"") => {
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$value.to_string()
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},
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_ => $value.into(), // <-- no getting rid of the into!
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}
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};
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}
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struct SomeStruct {
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first_name: String,
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//last_name: String, // NOPE because of @convert.
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//age: usize, // reason of .into() in the first place.
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}
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pub fn main() {
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let x = strinto!(SomeStruct {
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first_name: "First",
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//last_name: String::from("Last"), // NOPE 2.
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//age: 1, // NOPE 1. But I went further.
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});
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}
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// while this compiles for only &str "", it is also useless compared to into!
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// the reason is, that you cannot type check in the declarative macros.
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// while yes, you would conditionally run stringify!($value) in the match, but the match expansion
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// will always lead you to type errors if you don't do an .into() in the other arm.
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// also in the end it fails to compile for anything but all members of the struct being Strings.
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// the last idea was going with a helper trait, but that will bleed into the runtime code, and yet again only work on pure String structs.
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// I guess I have to embrace String::from(), .to_string(), .to_owned(), .into() madness, for something every human reader can deduce in a second,
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// if you would just implicitly convert &str to String if literally written in the code.
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// It is kinda amusing, that the other solution, to use new() kind of turns me off, because I cannot be explicit about the parameter name in the call.
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// I would literally love the option to be more explicit in function param names.
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// while builder patterns feel a bit bloated for static runtime options, i will probably look into automations for that.
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// this is probably the only aesthetic decision in rust I probably will hate forever.
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// It does not make sense, Strings as literals already are special in your code.
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// Because numbers are as well, you dont have to write 123.into() either.
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// I know I probably made some really harsh logical mistakes in my opinion here, and maybe it can be proven, that I am wrong, and I would love to hear that
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// However it kind of feels like an excuse to not simplify assigning declaratively written &str to Strings in the code.
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// And it makes sense to be explicit about creating a String Buffer sometimes, but it does not make sense mostly.
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// Anyway, I will still try a procedural macro for this, just for fun.
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